High resolution color cathode ray tubes (CRT's) commonly use a variable-voltage beam penetration phosphor technique to generate different colors. Post-accelerator voltage changes of several thousand volts are required to implement this technique. In high-speed, high-resolution color cathode ray tubes, it is desirable to switch between these voltages quickly and to accurately repeat the values of each of the voltages so that colors can be quickly switched and accurately reproduced.
The preferred embodiment of the present invention incorporates a tri-color cathode ray tube. The three DC voltages required to provide the three different colors are supplied by three DC voltage supplies. Each supply is selectively coupled to the cathode ray tube by an associated string of triacs activated by a corresponding trigger circuit. The rate of switching is determined and, if it exceeds a predetermined value, switching is inhibited.